1. Field of the Invention
The present invention relates to a semiconductor laser device employing group III nitride semiconductors.
2. Description of Related Art
Group III nitride semiconductors are group III-V semiconductors employing nitrogen as a group V element, and typical examples thereof include aluminum nitride (AlN), gallium nitride (GaN) and indium nitride (InN), which can be generally expressed as AlXInYGa1-X-YN (0≦X≦1, 0≦Y≦1 and 0≦X+Y≦1).
A blue or green wavelength laser source is increasingly used in the fields of an full color display, high-density recording in an optical disk represented by a DVD, image processing, medical equipment, measuring equipment and the like. Such a laser source is comprised of a laser diode employing GaN semiconductors, for example.
A GaN semiconductor laser diode is manufactured by growing group III nitride semiconductors on a gallium nitride (GaN) substrate having a major surface defined by a c-plane by metal-organic vapor phase epitaxy (MOVPE). More specifically, an n-type GaN contact layer, an n-type AlGaN cladding layer, an n-type GaN guide layer, an active layer (light emitting layer), a p-type GaN guide layer, a p-type AlGaN cladding layer and a p-type GaN contact layer are successively grown on the GaN substrate by metal-organic vapor phase epitaxy, to form a semiconductor multilayer structure consisting of the semiconductor layers. The active layer emits light by recombination of electrons injected from the n-type layers and positive holes injected from the p-type layers. The light is confined between the n-type AlGaN cladding layer and the p-type AlGaN cladding layer, and propagated in a direction perpendicular to the stacking direction of the semiconductor multilayer structure. Cavity end faces are formed on both ends in the propagation direction, and the light is resonantly amplified between the pair of cavity end faces while repeating induced emission, and partially emitted from the cavity end faces as laser beams.